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This article, written as a contribution to a festschrift for Paul Giannelli, surveys the development of the law on one type of feature-matching evidence that repeatedly attracted Professor Giannelli’s attention — “firearm-mark evidence.” By inspecting toolmarks on bullets or spent cartridge cases, firearms examiners can supply valuable information on whether a particular gun fired the ammunition in question. But the limits on this information have not always been respected in court, and a growing number of opinions have tried to address this fact.

The article explains how the courts have moved from a position of skepticism of the ability of examiners to link bullets and other ammunition components to a particular gun to full-blown acceptance of identification “to the exclusion of all other firearms.” From that apogee, challenges to firearm-mark evidence over the past decade or so, have generated occasional restrictions on the degree of confidence that firearms experts can express in court, but they have not altered the paradigm of making source attributions and exclusions instead of statements about the degree to which the evidence supports these conclusions. After reviewing the stages in the judicial reception of firearm-mark evidence, the article concludes by describing a more scientific, quantitative, evidence-based form of testimony that should supplant or augment the current experience-based decisions of skilled witnesses.